The computational density functional theory (DFT) investigating the CO gas adsorption on magnesium porphyrin nanorings (Mg4@PNR4).

The decorated butadiyne-linked four porphyrin nanorings with four magnesium cations (Mg4@PNR4) represented a novel class of nanoscale molecules. This Mg4@PNR4 system could be considered as a high surface area with favorable chemical and physical properties which has inherent ability to form hydrogen and covalent bonds. The Mg4@PNR4 system could contribute to air purification and greenhouse gas decrease by efficiently capturing toxic gases such as carbon dioxide and nitrogen oxides. This study aims to scrutinise and improve the CO gas sensing capacity of the Mg4@PNR4 system with four porphyrin rings using density functional theory (DFT). In all configurations, the adsorption values were negative which indicates adsorption process is physical and reversible. Also, the CO gas adsorption, in all configurations, increased the band gap of nanoring by 114-121 % and reduced the conductivity of the nanoring. Additionally, the recovery times were in the range of nano, pico and femto seconds which showed the rapid desorption of CO gas after physical adsorption. According to the NBO investigations, the amount of positive charge in the magnesium ions decreases and the positive charge in the gas increases during the adsorption of CO molecule on the nanoring. Eventually, the FMO analysis and the electron transfer amount (ΔN) showed that the electrons were transferring from CO to the porphyrin nanoring.